Generally, in a printed wiring board used in electronic equipments, when an electronic component is mounted on the printed wiring board, not only to prevent a solder from adhering on unnecessary parts, but also to prevent an exposed conductor of a circuit from being corroded by oxidation and humidity, a solder resist layer is formed in a region excluding a connection hole on a substrate on which a circuit pattern is formed.
Presently, a solder resist of the main stream is: one formed by using a photocurable resin composition; and another formed by using a thermosetting resin composition. In case of the photocurable resin composition, a light-irradiated part is cured, and a fine solder resist pattern is formed by removing another uncured part using a dilute alkali solution and an organic solvent.
Meanwhile, as a method for forming a solder resist pattern on a substrate using the thermosetting resin composition, the method for a screen printing of the thermosetting resin composition is employed, but this method is not suitable for forming a fine pattern. Therefore, it is common for forming a solder resist pattern using the thermosetting resin composition and producing a via hole for mounting to be performed by laser-irradiation. In particular, in cases where a fine solder resist pattern is desired, a carbon dioxide gas laser, an UV-YAG laser, an excimer laser or the like is used.
In case of forming a via hole by laser-irradiation, components (smear) of a solder resist film is without being decomposed and removed sufficiently, so that such a phenomenon that the components remain on the bottom of the via hole is generated. In case of remaining such a smear, in a subsequent plate processing, a non-deposition of plating part is generated to produce troubles such as bonding failure and the like when electronic components are mounted. Therefore, the process for removing the smear, so-called desmear process is required (for example, Patent Document 1).
In the desmear process, generally, after swelling with concentrated alkaline solution, a wet method in which a smear is decomposed and removed by permanganate solution is used.
In recent years, associated with decreasing weight and size of electronic equipments, as an interconnecting form of a chip and a printed wiring board, a flip-chip mounting capable of high-density packaging and reduction in the height of semiconductor packages rather than wire bonding is employed.
In the flip-chip mounting, a method for interconnecting between electrodes using a solder ball is widely known. Interconnecting with the use of the solder ball is performed by arranging the solder ball onto one of the electrodes of a wiring board or a chip and reflow after positioning another connecting electrode. Further, an underfill (a sealing resin) is flowed into a gap between the chip and the wiring board and the resultant is cured, thereby enhancing a reliability of connection. In order to reinforce a connection part, the underfill is filled to slightly overflow around from the gap between the chip and the substrate, so that skirts are formed regarding the chip as a top. However, since fluidity is designed to be higher in order to reliably fill the gap between the chip and the substrate, the underfill has a property of easily spreading on the solder resist. In particular, it is necessary that, in the high-density mounting, since the distance between devices around the other and the wiring system is short, the overflowing underfill reaches them, so as not to adversely affect the electrical actuation, to prevent the spread of the underfill.
As one of means of preventing the spread of the underfill, it is known a method of providing a dam in which a step of groovy or projecting part in the solder resist is formed to surround the flip-chip mounting part and then the overflowing underfill is dammed. For example, in Patent Document 2, a method of forming the step by scraping away the solder resist outside the vicinity of the outer edge of the chip using NC milling is heretofore proposed. However, this method is not sufficient to form a high-definition dam. In addition, Patent Document 2 discloses that a method of providing the groove around the chip by removing the uncured part of the photocurable resist. When the amount of underfill reaching the groove is insufficient, however, there is a problem that a conductor pattern located in the groove of dam is exposed unnecessarily. Further, in Patent Document 2, a method of forming a projection part (a projection piece) by applying a resist on a solder resist layer using a silk printing or the like is also heretofore proposed. However, in such method of forming by applying, it is difficult to form a high-definition projection part. Furthermore, Patent Document 2 discloses that the resist of the alkali development type and the UV-curable type can be used for such projection part, but it is no description of specific embodiments and examples including the advantage of the above-described case, the composition of the solder resist layer and the patterning method, and the method of specific realizations is not proposed.
On the other hand, a method of forming a projection part by printing the ink on a solder resist is heretofore proposed (for example, Patent Document 3).